The present invention relates to plastic lenses for spectacles, in particular to those having a high refractive index and a high Abbe's number and having good transparency, heat resistance, mechanical strength and impact resistance.
Plastics are being much used these days for optical products such as lenses, as being lightweight, hardly broken and easily colored when compared with glass. It is known to use, as the monomer material, an epithio group-having compound in producing plastic lenses. For example, Japanese Patent Laid-Open No. 180977/1999 discloses a plastic lens having optical properties, a refractive index of 1.70 or so and an Abbe's number of from 35 to 37 or so, which, however, still leaves room for improving its heat resistance and mechanical strength.
Japanese Patent Laid-Open Nos. 292950/1999 and 352302/1999 disclose a resin composition prepared by reacting an epithio group-having compound, an isocyanate group-having compound and a thiol group-having compound in a ratio of thiol group/isocyanate group of at most 1, and its use for plastic lenses. They say that the resin composition has improved heat resistance, mechanical strength and impact resistance. However, the plastic lenses of the resin composition are often cloudy and could not be well cured, and are therefore unsuitable to practical use for spectacles.
The present invention has been made so as to solve the problems as above, and to provide plastic lenses for spectacles having a high refractive index and a high Abbe's number and having good transparency, heat resistance, mechanical strength and impact resistance.